It has been determined that stator bar vibration, enabled by the radial clearance between the bar and stator slot, is a significant factor contributing to stator bar abrasion. The stator winding is designed and built with zero clearance in the slot. However, as a result of gradual shrinking of the slot contents such as bar armor, slot fillers and wedges, which can occur on a stator winding during normal, long-term operation, radial clearance develops in the stator slot. Early detection of the development of this clearance will enable generator owners to plan necessary corrective action before significant damage is done to the stator bar ground insulation due to bar abrasion. Thus, the jacking device will lend itself as a generator maintenance planning tool to identify parts and work scope for major maintenance outages.
The methodology used presently to measure the radial movement of the stator bar in the slot requires removal of the generator field from the stator. The cost of disassembly and removal of the field, the time it takes for this process, and the dangers of field removal have led to the omission of the radial movement measurement from outage schedules. A hydraulic jack with special jacking boards is typically used to push one stator bar against the radially opposite bar, and the movement is measured with a dial indicator.